Icelandic Contractor Uses Trimble Systems for Spillway and Dam Construction
Icelandic Contractor Uses Trimble Systems for Spillway and Dam Construction
Iceland is committed to growing its economy through the country‘s rivers and geothermal waters. In fact, Iceland is the only western country that produces all its electricity in the form of renewable resources like geothermal energy and hydropower. To keep pace with growth more resources are needed, Iceland has begun the construction of the new Búðarháls hydropower energy plant to feed clean electricity to power-intensive industries on the island.
Ístak was hired as the main contractor to build the power plant in the southern part of the Icelandic highlands. The project is located on the rivers Tungnaá and Kaldakvísl at Búðarháls, some 150 kilometers east of the country’s capital, Reykjavík. The project area extends over the Búðarháls ridge between the river Kaldakvísl and the existing Sultartangi reservoir. The design of the power plant channels water from the lake formed behind the two dams along a 4 kilometer tunnel cut through the Búðarháls ridge. The tunnel includes a 40 meter elevation difference and leads to the Búðarháls powerhouse. The completed powerhouse will have two 47.5 megawatt (MW) turbines totaling 95 MW installed. Once complete, this will create a rated discharge of 280 cubic meters per second (m³/s) to meet the estimated annual power output of 585 gigawatts per hour (GWh), which is comparable to the annual electricity consumption of Reykjavik.
One of the two 47,5MW turbines generating the power
Located between two older hydropower stations, Búðarháls is built on a section of the Köldukvísl River that is already being used for electricity production to minimize environmental impact. The construction of the plant included building two rock dams 1100 meters and 330 meters long respectively with a maximum height of 25 meters. These dams were constructed on the eastern side of the Búðarháls. The large quantity of water is then discharged from the powerhouse through a channel or tailrace. Ístak was hired to dredge the tailrace canal from the powerhouse out into the Sultartangi HEP reservoir.
The start of the 4km tunnel as viewed from the dam before it fills with water.
Lower end of the 4km tunnel looking towards the Budarhals Hydraulic Energy Power Plant.
Entry point for the water coming from the tunnel into the powerhouse to turn the turbines.
Looking to maximize productivity and meet extremely tight project deadlines, the team adopted seven Trimble GCS900 machine control systems with Dual GNSS Antenna. The machine control systems were loaded on excavators to build the power plant’s dams and trailrace which required excavating some 76,000 cubic meters of earth. The GCS900 system uses receivers and solid state angle sensors to measure the precise 3D position of the teeth of the bucket, which gives operators precise control during excavation. Machine guidance from Trimble was extremely useful considering excavation was primarily focused on digging underwater. Sand and silt from beneath the reservoir had to be removed in order to build the foundation for the dam walls. This means without automatic grade control, operators would not have been able to see the bucket and would have been basically be digging blind.
The two excavators equipped with Trimble GCS900 Grade Control System working on the dam.
For excavation and surveying the team also adopted VisionLink® from Trimble, an asset, fleet and site productivity management solution that helps track machine utilization and location, and material quantities and movement for improved job site productivity.
VisionLink Tracks Construction Productivity
GCS900 records as built data on the excavator during the construction process and sends the data to VisionLink for display and analysis. The GCS900 system also logs both positions of the bucket tips during the construction process and this recorded data is stored as TAG files on the machine control box. As data is captured, Istak can track the construction progress by comparing the as-built TAG files to the design, from anywhere, on any device, using the VisionLink web-based application.
“We learned from our local Trimble provider that in most cases, data collected from machines is sent over a cellular or Wi-Fi connection to Trimble‘s online file sharing web server Connected Community, then the data flows from there to VisionLink,” said Björn Sigþór Skúlason, Istak civil engineer. “Because of poor cellular reception, we transferred files from the excavator into VisionLink via USB. At the end of each shift we could then access machine data online to not only see how machines were being utilized, but to track the volume of material moved. This helped us accurately track the overall productivity on the jobsite.”
76000m³ spillway excavation as viewed in VisionLink on a smartphone live in the field.
More Accuracy Equals Greater Time Savings
The Istak team was pleased that they saved at least four days of surveying the tailrace with Trimble; a surveyor in a small boat with a sonar system attached to their GPS rover completed the survey work.
This is significant savings particularly because of the silt issues of the river floor. Silt and murky working areas generally cause problems for traditional survey and excavation methods. These environmental challenges can sometimes add days, and extra expense, to the process, explains Sigþór Skúlason.
“Due to the time it took for the silt to settle, our engineer accepted the machine as-built data and the results from the TAG files that the excavator collected,” said Skúlason. “Therefore, all volumetric information and then payment was calculated from the VisionLink system, which saved three days of work for the surveying staff. In all, VisionLink paid for itself on this single job and we would happily use it again.
VisionLink showing cut/fill information compared to the design. An applied filter makes that only the lowest elevations recorded by the excavator are visible.